The present invention relates generally to temperature sensing and, more particularly, to improving spatial resolution in a distributed temperature sensing system by the use of special sensor configurations.
Fiber optic Distributed Temperature Sensing (DTS) systems developed in the 1980s to replace thermocouple and thermistor based temperature measurement systems. DTS technology is based on Optical Time-Domain Reflectometry (OTDR) and utilizes techniques originally derived from telecommunications cable testing. Today DTS provides a cost-effective way of obtaining hundreds, or even thousands, of highly accurate, high-resolution temperature measurements, DTS systems today find widespread acceptance in industries such as oil and gas, electrical power, and process control.
The underlying principle involved in DTS-based measurements is the detection of spontaneous Raman back-scattering. A DTS system launches a primary laser pulse that gives rise to two back-scattered spectral components. A Stokes component that has a lower frequency and higher wavelength content than the launched laser pulse, and an anti-Stokes component that has a higher frequency and lower wavelength than the launched laser pulse. The anti-Stokes signal is usually an order of magnitude weaker than the Stokes signal (at room temperature) and it is temperature sensitive, whereas the Stokes signal is almost entirely temperature independent. Thus, the ratio of these two signals can be used to determine the temperature of the optical fiber at a particular point. The time of flight between the launch of the primary laser pulse and the detection of the back-scattered signal may be used to calculate the location of the scattering event within the fiber.
Distributed Temperature Sensing (DTS) has been used to monitor parameters such as, for example, temperature profiles in vessels or tanks as well monitor parameter on the surface of the vessel or tank.
In most DTS applications, current DTS systems use one or more of these sensors placed at various locations throughout. Each of these sensors has a resolution of about 1 meter, which may not provide an accurate measurement. Further, the use of the multiple sensors to compensate for the inaccurate measurement is expensive to manufacture and is physically and electrically complex, thus causing rise to reliability issues.
As the use of DTS systems expands there is an increasing need for systems with significantly improved spatial resolution. To a limited extent this can be achieved with more sophisticated DTS systems (electronics and software). But that avenue is limited in the quest for major improvements in spatial resolution. For major improvements new approaches in the deployment of the optical fiber are needed.
This need is met in the solutions to be described.